linux-kernel - Re: [PATCH v12 00/18] Enable FSGSBASE instructions

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Message-ID: <20200518061836.GA15641@infradead.org>
Date:   Sun, 17 May 2020 23:18:36 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Sasha Levin <sashal@...nel.org>
Cc:     linux-kernel@...r.kernel.org, tglx@...utronix.de, bp@...en8.de,
        luto@...nel.org, hpa@...or.com, dave.hansen@...el.com,
        tony.luck@...el.com, ak@...ux.intel.com, ravi.v.shankar@...el.com,
        chang.seok.bae@...el.com
Subject: Re: [PATCH v12 00/18] Enable FSGSBASE instructions

On Mon, May 11, 2020 at 12:52:53AM -0400, Sasha Levin wrote:
> Benefits:
> Currently a user process that wishes to read or write the FS/GS base must
> make a system call. But recent X86 processors have added new instructions
> for use in 64-bit mode that allow direct access to the FS and GS segment
> base addresses.  The operating system controls whether applications can
> use these instructions with a %cr4 control bit.
> 
> In addition to benefits to applications, performance improvements to the
> OS context switch code are possible by making use of these instructions. A
> third party reported out promising performance numbers out of their
> initial benchmarking of the previous version of this patch series [9].

The [9] reference can't be resolved anywhere in this mail.